A ache jaw can be many reasons, trauma to the bone and other variables. Its difficult to give a direct answer with out more information however I will suggest this.
Sinus - the sinus cavities are located near the jaw so when inflamed do to cold or other reasons this will cause your jaw to hurt. Benedryl should relieve some discomfort and of course always see a medical doctor.
Stress can cause all sorts of symptoms, such as sweating, flushing, difficulty in sleeping, loss of appetite, palpitations and stomach upsets. However, stress is not normally associated with an aching jaw, unless for some reason, you are grinding your teeth at night, or biting your teeth together very hard during the day, due to stress.
The only person who can really answer this question properly is your doctor, and if your jaw is always aching, this is really the person that you need to see.
If you doctor seems uncertain as to what is the cause of your jaw aching, you could insist on being referred to an orthodontist, who is a specialist in the teeth, the jaw area, and how this whole area functions.
It is possible that the aching jaw could be due to a problem in your bite, which sometimes happens when the upper and lower sets of teeth do not quite fit together properly.
The only way to answer these questions is to be examined by a doctor.